The present application relates generally to communication cables, and particularly to communication cables that allow transmission of both data and electrical power. A broad range of electrical cables and buffered optical fibers are installed in modern buildings for a wide variety of uses. These cables are used, for example, to provide data transmission between computers, voice communications, as well as control signal transmission for building security, fire alarms, and temperature control systems. Cable networks extend throughout modern office and industrial buildings, and frequently extend through the space between the dropped ceiling and the floor above.
Ventilation system components are also frequently extended through this space for directing heated and chilled air to the space below the ceiling and also to direct return air exchange. The space between the dropped ceiling and the floor above is commonly referred to as the plenum area. Electrical cables and fiber optic cables extending through plenum areas are governed by special provisions of the National Electric Code (“NEC”).
Because flame and smoke can travel along the extent of a plenum area in the event of electrical fire, the National Fire Protection Association (“NFPA”) developed a standard to reduce the amount of flammable material incorporated into insulated electrical conductors, fiber optic buffers and jacketing of cables. Reducing the amount of flammable material, according to the NFPA, would reduce the potential of insulation, fiber optic buffering, and jacket materials to spread flames and smoke to adjacent plenum areas and potentially to more distant and widespread areas in a building.
In 1975, the NFPA recognized the potential flame and smoke hazards created by burning cables in plenum areas and adopted in the NEC a standard for flame retardant and smoke suppressant cables. This standard, commonly referred to as “the Plenum Cable Standard,” permits the use of a cable without a conduit, so long as the cable exhibits low smoke and flame retardant characteristics. The test method for measuring these characteristics is commonly referred to as the Steiner Tunnel Test. The Steiner Tunnel Test has been adapted for the burning of cables according to the following test protocols: NFPA 262, Underwriters Laboratories (“U.L.”) 910, or Canadian Standards Association (“CSA”) FT-6. The test conditions for each of the U.L. 910 Steiner Tunnel Test, CSA FT-6, and NFPA 262 are: a 300,000 BTU/hour flame is applied for 20 minutes to 24-foot lengths of test cables mounted on a horizontal tray within a tunnel. The criteria for passing the Steiner Tunnel Test are as follows:
Flame Spread Requirement: less than 5 feet
Smoke Generation Requirements:                1. Maximum optical density of smoke less than 0.5        2. Average optical density of smoke less than 0.15 of fire retardant cabling        
This standard is one of the most stringent test methods for residential and commercial buildings. In plenum applications for voice and data transmission, electrical conductors and cables should exhibit low smoke evolution, low flame spread, and favorable electrical properties to pass the stringent requirements of copper data cables. Category 5e cables have evolved to provide even higher data transmission speeds with 10 gigabit per second cables, which are now designated Categories (“Cat”) 6, 6e and 6A. A Category 8, or a 40 gigabit per second cable, is being developed. Cables selected for plenum applications must exhibit a balance of properties and every component in a communications cable must perform its role.
Separators, jackets, insulations, buffer tubes and blown fiber tubing used in cables that meet the electrical requirements of Categories 6 and 7 must also pass the new norms for flammability and smoke generation. Tables 1 and 2, below, indicate categories for flame and smoke characteristics and associated test methods as discussed herein.
Fiber optic cables and fiber optic blown tubing, which are used in the plenum areas of buildings, must adhere to the same flame retardancy and low smoke characteristics of the NFPA 262 Plenum Test. Underwriters Laboratory (UL 2885) is a test method for determining whether components or materials of a cable can be designated as a non-halogen cable. Underwriters Laboratory (UL 2885), titled Acid Gas, Acidity and Conductivity of Combusted Materials and Assessment, uses IEC 60754-1, IEC 6074-2 and IEC 62821-1 to benchmark “all materials” within the cable design, i.e., insulation, spline or crosswebs, tapes or other cable fillers, fiber optic buffer and the overall jacket. Based on these test methods, a determination can be made for the presence of halogens, e.g., chlorine, bromine and fluorine. Test protocol 62821-1 Annex B, determines the presence of a halogen using the Sodium Fusion Procedure as described in Part 5.3 IEC 62821-2, i.e., Chemical Test: Determination of Halogens—Elemental Test.
Materials evaluated to IEC 62821-1 Annex B Assessment of Halogens Required for extruded material.
The test protocol consists of the following stages:
Stage 0: Determination of Halogens—elemental test for chlorine, bromine and fluorine using the sodium fusion procedure as described in part 5.3 of IEC 62821-2 (Chemical Test: Determination of Halogens—Elemental Test). If the results for chlorine or bromine or fluorine are positive, proceed to Stage 1.
Stage 1: Test according to 6.2.1 of 60754-2 for pH and Conductivity. If the pH is ≥4.3, the conductivity is >2.5 μS/mm and ≤10 μS/mm, proceed to Stage 2.
Stage 2: Test according to 6.1.1 of 60754-1 for chlorine and bromine content expressed as HCI. If the result if ≤0.5%, proceed to Stage 3.
Stage 3: Test for the determination of low levels of fluorine as described in part 45.2 of IEC 60684-2 (Determination of low levels of fluorine) Methods A (Ion selective electrode method fluoride) or B (Alizarin fluorine blue method).
The European standards have similar goals of fire retardant and low smoke generation cables. Polyvinylchloride, a halogenated material, remains a dominant jacketing grade throughout the European cable community. The standards which have evolved are the so-called International Classification and Flame Test Methodology for Communications Cable. Based on these evolving standards, a new list of acronyms has evolved, albeit with much similarity to the North American standards.
These Euro-classes for cables measure the following:                A. Flame Spread=FS        B. Total Heat Release=THR        C. Heat Release Rate=HRR        D. Fire Growth Rate=FIGRA        E. Total Smoke Production=TSP        F. Smoke Production Rate=SPR        
The European International Classification and Test Methodology for Communication Cables is shown below in Table 1 and it is shown in an abbreviated form.
TABLE 1The European International Classification and Test Methodology for CommunicationCablesClassTest MethodsClassification CriteriaAdditional ClassificationAcaEN ISO 1716PCS ≤2.0 MJ/kg (1)Note: Mineral filled circuit integrity cableB1caEN 50399 (30 kWFS ≤1.75 m andSmoke production (2, 5) and Flamingflames source)THR1200 ≤10 MJ anddroplets/particles (3) and Acidity (4, 7)andPeak HRR ≤20 kW andFIGRA ≤120 Ws−1EN 60332-1-2H ≤425 mmB2caEN 50399 (20.5 kWFS ≤1.5 m andSmoke production (2, 5) and Flamingflames source)THR1200s ≤15 MJ anddroplets/particles (3) and Acidity (4, 7)andPeak HRR ≤30 kW andFIGRA ≤150 Ws−1EN 60332-1-2H ≤425 mmCcaEN 50399 (20.5 kWFS ≤2.0 m andSmoke production (2, 6) and Flamingflames source)THR1200s ≤30 MJ anddroplets/particles (3) and Acidity (4, 7)andPeak HRR ≤60 kW andFIGRA ≤300 Ws−1EN 60332-1-2H ≤425 mmDcaEN 50399 (20.5 kWTHR1200s ≤70 MJ andSmoke production (2, 6) and Flamingflames source)Peak HRR ≤400 kWdroplets/particles (3) and Acidity (4, 7)andandFIGRA ≤1300 Ws−1EN 60332-1-2H ≤425 mmEcaEN 60332-1-2H ≤425 mmFcaNo Performance Determined
Table 2, below, provides a listing and comparison of the North American standards and the European standards from most stringent flame retardancy and low smoke requirements to least stringent.
TABLE 2A comparison of North American & European Fire Performance Standardsfrom most severe to least severe for Communications CablesNorth America StandardEuropean StandardNorth American Test ProtocolsEuropean Test ProtocolsMost SeverePlenum TestClass B1Steiner Tunnel - 88 KWClass B1 30 KW Flame SourcesUL 910LAN Comm. Cables300 BTU @ 20 minutes plusFS <1.75 m, THR <10 mgNFPA 262EN 50399-30 KWsmoke peak <.5Peak HRR <20 KWFT-6EN 60332-1-2Average <.15FIGRA <120 WSCMPSevereRiser TestClass CRiser Test - 154 KWClass C 20.5 KW Flame SourceUL 1666EN 50399-10..5 KW &527 KW @ 30 minutesFS <2.0 m TGR <30 m;FT-4EN60332-1-2Peak HRR <60 KWCMRFIGRA <300 WSLess SevereGeneral Purpose TrayClass DGeneral Purpose 20.5 KWClass D 20.5 KW Flame SourceCable TestIEC 60332-370K BIT @ 20 minutesTHR <70 m;UL 1581EN 50399-20.5 KWPEAK HRR <400 KWFT-2/CMFIGRA 1300 WSLeast SevereVW-1Class EBunsen Burner TestClass EFT-1IEC 60332-11 minute (15 seconds flame)H <425 mm
In addition to the requirement of low smoke evolution and flame retardancy for plenum cables, there is a growing need for enhanced electrical properties for the transmission of voice and data over twisted pair cables. In this regard, standards for electrical performance of twisted pair cables are set forth in the Telecommunications Industry Association (TIA) and American National Standards Institute (ANSI) in ANSPTIA-568-C.2. Similarly, the standards for data transmission over optical fiber cables are covered in ANSPTIA-568-C.3.
A balance of properties or attributes is needed for each component (e.g., insulation, buffer, cable fillers, fiber optic strength member, fiber optic blown tubing and jacketing) within copper and fiber communications cable so that it can meet the electrical performance of copper cabling or the transmission characteristics of fiber optic high speed data cable and pass the NFPA 262 Flame and Smoke Requirements, the NFPA 259 flame requirements and similarly the European standards for Class B and Class C.
Optical fiber cables exhibit a set of needs that include unique mechanical properties to prevent damage to the fragile glass fibers. These needs are evolving for hybrid copper and fiber designs, Passive Optical Networks (PON) or Power over Ethernet (PoE). For instance, PoE will generate more heat as it provides data transmission as well as power to LED lighting, wireless interface points, cameras and is employed in a wide range of other applications, whereby temperature control and office automation can be accomplished remotely from interactive phones and computer devices.
PoE relates to a system in which electrical power can pass safely along with data on cables (e.g., Ethernet cables). IEEE 802.3af—2003 standard provides for up to 15.4 watts of DC power and can operate with Category 3 cables at this low power requirement. IEEE 802.3 at—2009 standard also known as PoE+ or PoE plus provides for 25.5 watts of power over Category 5 or higher.
There remains a need for a communications cable that can operate reliably while minimizing or eliminating cross-talk between conductors within a cable or alien cross-talk between cables, and also a need for separators for use in such telecommunications cables, while meeting the design criteria described above. There also remains a need for a communications cable that can provide low smoke generation and overall flame retardancy, e.g., as required by the NEC for use in plenum and riser areas of a building.